The practice of protecting buildings against fire using an array of automatically-released sprinklers, interconnected to form a sprinkler system, has been used for many years. In recent years, an increasingly large percentage of new industrial buildings has been equipped with this type of protection. In its basic form, a sprinkler system consists of a network of pipes, which are charged at one end with a fluid under pressure from a fluid-supply source, interconnected with a series of branch lines which support the sprinklers. Generally there is a check valve between the fluid supply and the input of the sprinkler system piping, which prevents the possibly contaminated sprinkler fluid from backing up into the supply under conditions in which the supply pressure is low. This check valve also causes the peak pressure of the fluid supply to be "trapped" and stored in the sprinkler system. Each sprinkler contains an element which melts or breaks at a certain elevated temperature, causing a rapid release of fluid in a controlled pattern to extinguish the fire that originally caused the elevated temperature. Generally a sprinkler has no automatic shutoff provision, hence after the fire has been extinguished, the sprinkler fluid continues to flow, but types of sprinklers which automatically restore to a normal off condition after the sensed temperature has returned to normal recently have come into use. Most generally the fluid is water.
It is important to summon the fire department whenever a sprinkler has released because (1) a sprinkler is not 100 percent effective in putting out a fire, and it is possible that even with the sprinkler operating normally, the fire can grow to an uncontrolled level, and (2) a substantial amount of secondary damage can be caused by the continuous flow of water from the open sprinklers, if the water supply is not shut down. The sprinkler system, therefore, must have provisions for initiating a fire alarm upon release of water from one or more sprinklers.
There are a number of devices currently employed for providing an alarm when one or more sprinklers of a sprinkler system release. Although many of these devices provide an alarm if one or more sprinklers release, they have their disadvantages, such as relatively slow speed of response, relatively high equipment or intallation cost, and susceptability to false alarms (for example from a temporary waterflow resulting from city pressure surges compressing the air trapped in the sprinkler system).
It is an object of this invention to provide a sprinkler flow detector which is very high in speed of response, low in equipment and installation cost, and is highly immune to stimuli that can cause false alarms. Other objects of the invention include providing a detector which exhibits high detection reliability and can function properly in systems which use fast automatically-restoring sprinklers.